Evacs Versus Flate plate collectors

[Paul Bailey]

For those in the two camps here ... the Evacuated tubes Versus the Flat plate solar thermal collectors, I thought I'd post a pic with good representation of Efficiency curves for both in differant heating applications., Again remember that they Both have there Pros and Cons.Paul:)

[Art Toy]

Hello Paul.

Do you have the data source for this graph?
May I copy the graph?

Thanks, Art.

[Paul Bailey]

Welcome to Greenpowertalk Art> I think I picked this up From Caleffi in Spain. A nice Pic demonstrating not just the product but how the application and design are SO closely tied to get much higher Efficiencies that would otherwise be lost and never realized unless your in the Know!!!! Some real nice stuff...there products and info. Search away> Paul:)

[Rob Beckers]

"Evacuated tubes Versus the Flat plate solar thermal collectors", them are fighting words in some parts of the RE community Paul! ;)

My advise is to be careful in reading too much into the rather abstract depiction of plate vs. tube. For one, all the evacuated tube collectors start at an efficiency of around 50% (that's the left side of that graph, where it hits the Y-axis). Not the 80% the graph depicts. For example, the popular Apricus tubes start at 42%, Viessman (a high-end brand) starts at 51%. For the flat plate collectors the numbers are around 70% for most, with a few of them in the high-70%'s. For example Enerworks, a popular Canadian brand over here, has a maximum efficiency of 77%.

What that means is that the intercept, where evacuated tube outperforms flat plate, is much further to the right in the graph than it is depicted. For the better flat plate vs. the better evacuated tube it's over 100F temperature difference (that's 38 Centigrade). You can find the numbers for most brands in a very nice article in the last Home Power Magazine (http://www.homepower.com/home/) (issue 123), the same numbers are also on the SRCC web site (http://www.solar-rating.org/SUMMARY/Dirsum.pdf) (they do the independent testing).

I just got back from an RE workshop and had a chat with one of the flat plate manufacturers about the pros and cons of each. The upshot is that both have their advantages and issues, neither is a clear winner, not even in the Canadian climate we have over here. One difference is that flat plate is a whole lot cheaper for the same effective surface area than evacuated tube.

-RoB-

[Paul Bailey]

Again another photo from Caleffi re the Evac wars. This one is is collector representation Vs the implied heating application as the one above. Paul:)

[Randy Lacey]

Hi Paul,

Is the graph suggesting that flat plate collectors are more efficient at lower temperatures than the evacuated tubes?

Thanks
Randy